The invention relates to propylene polymer single or multilayer pipes for pipelines with improved resistance to rapid crack propagation as well as to a process for producing them.
Olefin polymer pipes for pipelines consisting of ethylene polymers (Conference Papers “Plastic Pipeline Systems for the Millenium” Göteborg 1998, p. 841-842) or propylene block copolymers (Conference Papers “Plastic Pipeline Systems for the Millenium” Göteborg 1998, p. 611-620, 841-842) are known.
The disadvantage of pipelines made from conventional polypropylene pipes is the insufficient resistance against rapid crack propagation in pressure applications at and below room temperature or even below temperatures up to 40° C. Any small crack formed may propagate many kilometers causing complete destruction of the pipeline with obvious danger to the public. For a service temperature of for example 0° C., pipelines made of conventional polypropylene pipes have a critical pressure of approximately 1 bar, which is considerably below the normal service pressure.